EL display devices including an EL element, which is based on electroluminescence (hereinafter referred to as EL) of an organic or inorganic material, have been attracting attention, as EL display devices have a higher response speed and a wider viewing angle than liquid crystal display devices.
EL elements are, however, typically susceptible to, for example, water and oxygen. EL elements react with even a small amount of water or oxygen, which degrades the properties of the EL elements and shortens the life of a display device including such an EL element.
EL elements are roughly classified into organic EL elements, which include an organic substance for a light-emitting layer, and inorganic EL elements, which include an inorganic substance for a light-emitting layer. An organic EL element includes an organic EL layer containing a light-emitting layer as well as a lower electrode and an upper electrode that sandwich the organic EL element. An inorganic EL element includes, for example, a light-emitting layer and dielectric layers sandwiching the light-emitting layer as well as a lower electrode and an upper electrode that sandwich the three layers.
Entry of, for example, water or oxygen into such an EL element leads to, for example, oxidation or hydroxylation of a component such as the light-emitting layer or upper electrode or to crystallization thereof. This results in a dark spot, that is, a non-light-emitting spot, and/or in a shrinkage, that is, a non-light-emitting region expanding and a light-emitting region shrinking accordingly. Dark spots and the shrinkage are known to shorten the life of EL elements. Thus, there is a need to minimize, for example, entry of water or oxygen into EL elements.
In view of the above, there has been known a technique of, for example, forming a sealing layer on an EL element to seal up the EL element for prevention of entry of, for example, water or oxygen into the EL element (see, for example, Patent Literature 1).
Such a sealing layer is made up of an inorganic layer or a stack of an inorganic layer and an organic layer. The inorganic layer has the function of preventing entry of water for moisture prevention, and thus serves as a barrier layer. The organic layer is used as a buffer layer (stress relaxation layer): It relaxes stress on the inorganic layer, covers a pinhole, and/or prevents a crack in and peeling of the inorganic layer when it is being disposed.